TRX2A Potential builder questions

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TRX2A Potential builder questions

Postby KF7DRU » 15 Jul 2012 02:02

Hello, All.
I am interested in building the JUMA TRX2A transceiver.

I have a question about antenna blanking. I have a Pixel Pro-1B, that is used as a receive only antenna. It uses a preamp that has the capability of being blanked when a nearby
RF antenna is transmitting. It is designed to be connected to a key out from the transmitter, that has a voltage level change to indicate the transceiver is transmitting. Signal level is low ( <0.7 V) high (> 1.2 V). The polarity of the signal is configurable in the preamp. Is there any way that the TRX2A transceiver can output such a signal?

Also, I am very interested in using the Juma as a SDR. I can't seem to find much info on how this works for others. Are there some users that have used the IQ outputs?

Thanks for any information you can provide me.

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Joined: 14 Jul 2012 06:09
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Re: potential builder questions

Postby 5B4AIY » 20 Jul 2012 15:08

Hi, Dave,
First, antenna blanking. The Juma outputs a DC voltage on the antenna output when in the transmit mode. This voltage is used by the companion PA-100D linear amplifier as the transmit enable signal, and switches the amplifier from its bypass mode into its active transmit mode. The first schematics is the Juma-TRX2 HF SSB/CW Transceiver All Band 10W Power Amplifier Circuit Diagram, Rev A3. In the bottom right-hand corner you will see the TX signal. This is a +5V logic signal the is asserted when the transmitter is active in the Tune, SSB, or CW modes. This +5V logic level turns on TR6, and the drain voltage goes low. This in turn turns energises RL-1C via TR7. The +12V energising voltage of RL-1C is used as the final amplifier bias voltage via R57, Z1, D7 and D8, and is also T14. This voltage is fed via R58, 100R, decoupled and bypassed to RF by C23, 100nF, and then fed out on the ANT socket via R36, 10K. If you were to connect a suitable RF choke to the antenna output and decouple the 'cold' end to RF, you would then have access to a 12V DC voltage at a current of up to about 1mA which could then be used to switch a transistor or other device for active receive antenna desenitisation purposes.

Your second point regarding the use of the TRX-2 is that really this transceiver is not a Software Defined Radio as is conventionally understood. For example, a Flex-3000 or SDR-CUBE. It is an analog direct-conversion SSB/CW transceiver which is provided with an auxilliary I/Q output from its phasing detector. There is no digital signal processing taking place. Although the microprocessor is well-suited to DSP, none of this capability is used, neither the RF input signal nor the demodulated audio signals are digitised and processed. The microprocessor is used primarily as a convenient user interface for the Direct Digital Synthesiser chip used to provide the I and Q local oscillator signals for the Tayloe detector and SSB generator as well as providing a User Interface system to display the various operating modes and parameters, and to control the CW keyer and the various filters and other control aspects. The internal 12-bit A-D convertor of the microprocessor is used to measure the DC voltage, amplifier drain current, and forward and reverse output powers, as well as the level of the received signal for S-meter purposes. This statement is not meant in a disparaging manner - far from it - the technical achievement of designing a stable SSB platform using novel wide-band phasing techniques and providing a receiver performance well on a par with many other commercial transceivers is a great credit to both Juha and Matti. As an engineer myself, I take my hat off to them, this is fantastic little transceiver - but it's not a SDR. If you need any more technical information, let me know, I'll be happy to explain to whatever detail you need.
73, Adrian, 5B4AIY
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Re: potential builder questions

Postby N7KG » 14 Aug 2012 20:03

I am curious about the SDR as well. I was wondering if it would work to port the I/Q of the TRX2/A out to SDR software. Has anyone done this, successfully or not? Thanks

Brettt, N7kg
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Joined: 09 Aug 2012 07:08
Location: USA

Re: potential builder questions

Postby KH2BR » 15 Aug 2012 19:27

I really like sdr-radio with my fifi. I also tried it with the trx2a. I had to fool the software into believing the sdr radio had a SI-570 by plugging a soft rock into a USB port. I was able to control frequency by selecting external radio and controlling the dds vfo, and listen to signals and got diverted to other fun projects. Just try everything and have fun and don't get diverted like I did with this new iPad.
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